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Discussion Starter · #1 ·
I have posted regarding this issue before but it has been a while and I am at my wits end. For the record the one certified Triumph mechanic in the state can't seem to troubleshoot the problem and insists it is running fine, or at least that's what the computer tells him.

Bike: 2010 Bonneville SE, 17,000 miles, Arrow exhaust (tunes as such) with AI removed.

Problem: I am getting back fire, sputtering, sometime lurching (fairly minor but still a safety issue at times) only when decelerating at low RPMs just before the throttle is full closed. When rolling on, no problem at all. Throttle full close, no issues. It is only when rolling off and always with the throttle just a tad open. Prior to the issue the idle was as smooth as a metronome but it does idle a little irregular now but primarily when cold.

I changed out the MAP sensor as that was an inexpensive endeavor. Changed out plugs, they were of course a little carbon fouled due to the issue in question (I presume). Old timer I met at the bar is somewhat convinced it is dirty injectors, which might very well be possible as I haven't exactly been consistent on gas treatment over the winter months (hangs head in shame).

Basically I am looking to figure it out through the process of elimination starting with the cheap stuff first. I have pretty much given up on taking it to the dealer again.
 

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Check all your vacuum caps and rubber pieces, make sure they are not cracked or torn. Also check your air cleaner and air box.
 

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Going from low RPM to idle is taking the bike from closed loop to open loop. You may have an issue with your O2 sensors.
 

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Discussion Starter · #4 ·
Air cleaner and box checked just fine on initial inspection when the problem began. Worth looking over again.
 

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Discussion Starter · #6 ·
Going from low RPM to idle is taking the bike from closed loop to open loop. You may have an issue with your O2 sensors.
That certainly has crossed my mind but as they are not exactly cheap, I thought I might eliminate some other possibilities first. I would think those would trigger a fault but giving them a cleaning might be a good start. Sounds like there are mixed opinions on the effectiveness of cleaners.
 

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Discussion Starter · #7 · (Edited)
I have read your post previously and it is what lead me to replace the MAP sensors (again, cheap repair) and as far as I can tell the mechanic has everything sealed up well.

Hadn't considered blockage to the sensor. Sounds like the logical next step. Thank you! Something related to the MAP sensor has been my suspicion based on the bikes behavior but my mechanic/troubleshooting skills suck arse. Do mechanics not refer to Forchetto's posts when they are stumped? Very frustrating.
 

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Another component that can be causing an over-rich issue is the oil temperature sensor. This acts like a automatic choke enriching the mixture if it senses the oil/engine is cold. If it's out of spec it could be enriching continuously, sample thread where that was found to be the culprit:

http://www.triumphrat.net/air-coole...-efi-coils-options-for-single-tower-apps.html

More info about it:

http://www.triumphrat.net/twins-tec...ng-this-morning-fuel-issue-3.html#post2605129

http://www.triumphrat.net/air-coole...d-oil-temperature-sensors-on-efi-bonnies.html
 

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I had similar issues recently and went over everything on my bike - no error codes or engine management light, so it was a real pain to work out. By chance I discovered the fault using TuneECU. Do you have this software plus a suitable cable? (do a search if not - software is free, a suitable cable is cheap). Using TuneECU, check that the voltage of the Throttle Position Sensor is roughly 0.6v at idle. Mine was faulty, and way out of spec, but not throwing an error code. Was causing me major running issues much like your symptoms. Replacement fixed it and was an easy job.
 
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